PERFORMABILITY ANALYSIS OF OPERATION MODES OF CONFIGURABLE DUPLEX SYSTEMS.

Abstract

Configurable duplex system structures, like the IBM 3084, are capable of operating as one single system (single-image modes) or as two independent systems (partitioned mode). The user installation has a choice of operation modes. The single-image mode of operation is more tolerant of hardware failures because of component redundancies, but on operating system failure all processors are lost. In the partitioned mode the outage of hardware component or operating system brings down the affected half of the duplex system. The problem is to select the mode of operation. Areas where one of the operation modes is better than the other are delineated. The sensitivity of the choice of operation mode to the goals of the installation (choosing on the basis of average or percentile) is also demonstrated. The use of a steady-state performability measure instead of transient performability is shown to distort the choice of operation mode. Hence, simple-to-compute tight upper and lower bounds for the hard-to-compute transient performability are derived.